The overall objective of the proposed research is to provide an experimental analysis of the effects of drugs of abuse on sensory and motor function in non-human primates. Animal psychophysical procedures will be employed to obtain quantitative assessments of drug-induced changes in the following aspects of sensory function: 1) absolute auditory thresholds; 2) absolute visual thresholds; 3) discrimination of synthetic speech sounds (steady-state vowels); and, when indicated, 4) auditory frequency-difference limens. For each of these aspects of sensory function, motor function will also be assessed by examining reaction times to each type of sensory stimulus employed. All experiments will be conducted using a standards reaction time procedure with non-restrained laboratory baboons. The proposed research will emphasize the effects of combinations of ethanol with both marijuana extract and its main constituent, delta-9-THC. Additionally, basic studies will also be conducted on the effects of acute administration of the opioid agonists, antagonists, and mixed agonist-antagonists. The results will provide normative data on the effects of drugs of abuse on sensory and motor function across a range of drug doses, and on the interaction effects of the two most commonly abused compounds, ethanol and marijuana. The study will also provide information relevant to drug scheduling and clinical evaluation of functional decrements produced by these compounds.